The present invention generally relates to pneumatic tires, specifically radial tires with a very low aspect ratio.
The sidewalls of conventional pneumatic tires provide these conventional tires with desirable flexibility in the radial direction. This radial flexibility allows the tread surface to move radially inward to accommodate irregularities in the road surface. However, the sidewalls of conventional tires also limit the performance of the tire with undesirable lateral and circumferential flexibility. Lateral sidewall flexibility limits the responsiveness of the tire in cornering, and circumferential flexibility limits the tire""s capacity to handle the torsional forces encountered in acceleration and deceleration. In addition, the space required for the sidewall limits the maximum size of the wheel and the size of the brake mechanism that can be fit within the wheel for a given overall tire diameter.
When normally inflated, the sidewalls of conventional tires protect the rim from possible contact with the road surface. Also, conventional sidewalls distribute the weight of the vehicle and the force of impacts with road hazards by acting in tension to confine the compressive force provided by the air in a normally inflated tire. However, when normal inflation air pressure is lost, such as when the tire is punctured, the relatively thin and flexible sidewalls of a conventional tire collapse and buckle in such a manner that the sidewall fails to provide its normal functions of radial flexibility, rim flange protection, or the distribution of forces from the wheel to the road.
Conventional radial ply tires with low aspect ratios have been developed in part to address the limitations of sidewalls. As noted by U.S. Pat. No. 4,811,771, (""771), there are basically two different shapes of passenger tires on the road today: high aspect ratio tires (aspect ratio greater than 69) and low aspect ratio (aspect ratio less than 70) tires. The low aspect ratio tires, where the radial depth of the sidewall is reduced relative to the tread width, have better cornering characteristics and less rolling resistance than the high aspect ratio tires. Patent ""771 discloses the use of a special low aspect ratio tire (aspect ratio of 40 to 45) used in conjunction with a new larger diameter wheel (18 to 20 inches).
Recognition of the advantages of reducing the radial depth of the sidewall is not new. U.S. Pat. No. 1,293,528, discloses the use of a plurality of chain rings as an xe2x80x9cinexpansiblexe2x80x9d bond to provide a pneumatic tire having a cross section under inflation to present a most advantageous width for weight carrying capacity and which will have only the minimum radial depth necessary to provide the requisite cushioning action, so that the wheel rim may be as close as practicable to the surface traveled over and the driving power thereby most efficiently transmitted.
U.S. Pat. No. 1,456,062 discloses a tire that has no straight sidewalls or belly part, independent of its wide gable-like tread, as in existing types of inflated tires. In fact the whole of the tire cover, with the exception of its suitable inextensible base beads is a shock absorbing tread, which xe2x80x9cmay be used to replace existing types of solid rubber band tiresxe2x80x9d. The tread is arced, with a narrow blunt apex on its centerline, so that the footprint varies in size with the applied load. As best it can be determined from the description in this 1923 patent, the tire does not have belts or beads in the same sense as modern-day tires. The patent mentions xe2x80x9cinextensible base beadsxe2x80x9d but describes and illustrates these beads as being part of xe2x80x9can abnormally strong and preferably thin supple foundation . . . which may be manufactured from woven cord and be endless and abnormally strong in every direction.xe2x80x9d As described, the tires appear to have aspect ratios somewhere around 48%. This unbelted, non-radial ply tire also provides rim flange protection and limited runflat capability as seen in the Patent""s FIG. 3, where the flattened, deflated tire is thick enough to support the vehicle by pressing against the substantially flat well of the wheel without loading the wheel rim flanges.
Other patents describe tires, such as racing tires, with aspect ratios as low as 25% but still having sidewalls. For example, German Pat. No. 25 34 840 discloses a low aspect ratio tire with a running tread having a width which is at least half the total width of the tire, and preferably less than two-thirds of the total width of the tire. The remainder of the tire width comprises sidewalls which are radially diverted towards the seating surfaces of the tire rim.
German Pat. No. 2 127 588 discloses a very low profile pneumatic tire for racing cars (aspect ratio less than 25%) having a broad tread moulded in a concave shape so that it becomes flat when the tire is inflated at low pressure. The maximum width of the rim is 120% of the wheel diameter. The tire may be of radial or crossply construction. The sidewalls are substantially flat and vertical in an un-inflated tire.
While it may not be apparent, there exists a potential to develop a pneumatic radial tire with revolutionary dimension properties providing superior performance when compared to conventional pneumatic radial tires. The challenge is to develop such a tire combining improved handling and performance with adequate radial flexibility, sufficient rim flange protection and enhanced runflat capability suitable for use on conventionally-shaped (i.e., standard) wheel rim designs.
The tire of the present invention embodies radical dimensional properties applied to a pneumatic radial tire having a tread area comprising a ground contacting tread and a circumferential belt structure that is directly joined to the bead areas of the tire without sidewalls, providing the tire with an aspect ratio of less than 50 and preferably less than 25. Each bead area comprises a bead foot compatible with a standard wheel rim shape and at least one inextensible annular bead. The tire has a carcass structure comprising at least one cord reinforced elastomeric ply layer, the cords of each ply layer having a more or less radial orientation, the ply layers extending laterally between the two bead areas and radially inward of the belt structure. The bead areas also have rim flange protectors comprising continuous circumferential elastomeric projections extending laterally outward from the bead area and adjacent to and radially outward of the wheel rim flanges. Because the relatively thin and flexible sidewall structure is eliminated in the tire of the present invention, the tire maintains structural integrity while uninflated. The addition of elastomeric reinforcing material of sufficient thickness and strength to the area where the bead areas are joined to the tread area will allow the tire to support the weight of a vehicle and provide extended runflat operation.
The tire of the present invention may use one or more carcass plies that may be turned up around the beads in each bead area. Also the bead areas may comprises elastomeric apexes, chafers, chippers and/or flippers. The tread and belt structure can be extend radially and laterally outward from the bead with an elastomeric shoulder wedge located radially outward and adjacent to each bead area and radially inward of the belt structure.
A preferred embodiment of the tire of the present invention operationally fits on a conventionally-shaped wheel rim which is from 2 to 5 inches (51 to 127 mm) wider than a standard automotive tire rim, and which also has a nominal rim diameter of from 4 to 6 inches (102 to 152 mm) more than the standard wheel rim. For example, the tire could be a P210/20R19 tire on a 7.5J19H2 rim.
Reference will be made in detail to preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. The drawings are intended to be illustrative, not limiting. Certain elements in selected ones of the drawings may be illustrated not-to-scale, for illustrative clarity.
Often, similar elements throughout the drawings may be referred to by similar references numerals. For example, the element 199 in a figure (or embodiment) may be similar in many respects to the element 299 in an other figure (or embodiment). Such a relationship, if any, between similar elements in different figures or embodiments will become apparent throughout the specification, including, if applicable, in the claims and abstract. In some cases, similar elements may be referred to with similar numbers in a single drawing. For example, a plurality of elements 199 may be referred to as 199a, 199b, 199c, etc.